This invention relates to an office-type chair, and more specifically relates to an improved synchrotilt mechanism coupled to the seat and back of the chair for providing improved seating comfort.
Office chairs conventionally provide some type of rearward tilting movement. In its simplest variations, the rear tilting involves solely the back, or the seat and back as a unitary construction. To provide improved and more desirable tilting movement and seating comfort, however, many office-type chairs employ a synchrotilt mechanism coupled between the chair base and the seat-back assembly, for permitting the seat and back to simultaneously tilt at different rates, with the tilt rate and maximum tilt angle of the back typically being about twice the tilt rate and maximum tilt angle of the seat.
Chairs employing synchrotilt mechanisms for permitting simultaneous but relative tilting of the seat and back are well known, and numerous mechanisms have been developed for performing this function. Most of these mechanisms, however, have caused relative motion between the chair and the seated occupant which has interfered with occupant comfort. Such relative motion may involve relative sliding between the seat and the occupant""s hips or thighs, and/or sliding between the chair back and the occupant""s back, during the relative tilting between the seat and back. In an attempt to alleviate or at least partially compensate for this problem, several chair mechanisms have been developed which cause the seat, during rearward tilting of the seat-back arrangement, to tilt relative to the back about an axis located approximately at the hip axis of the seated occupant. This hip axis is disposed in upwardly spaced relation from the rear portion of the seat, and spaced forwardly from the lower portion of the chair back. While locating the relative tilt axis between the seat and back at the occupant""s hip axis is believed to provide improved performance, particularly with respect to minimizing the relative sliding motion between the seated occupant and the seat/back, nevertheless many of these known mechanisms still fail to provide the degree of performance desired, particularly with respect to the desired comfort and ease of movement (often referred to as xe2x80x9cridexe2x80x9d) associated with tilting of the chair.
Accordingly, it is an object of this invention to provide an improved synchrotilt mechanism for a chair which is believed to provide improved control over the relative but synchronized tilting of the back and seat during tilting of the seat-back assembly so as to provide improved occupant comfort and ride while providing improved performance with respect to minimization of the relative sliding movement between the seated occupant and the back and/or seat of the chair.
More specifically, in the improved chair of the present invention, the chair back is supported on a rigid upright assembly which includes lower lever arms which project under the chair seat and are coupled at forward ends thereof to a horizontal tilt shaft which is disposed under the front of the chair seat and is supported on a control housing fixed to the upper end of the base pedestal. A conventional tension control mechanism is disposed in the control housing and coupled between the tilt shaft and the control housing for normally urging the upright arrangement, and the chair back, into an upright position. The chair seat is movably supported on the lower lever arms of the upright assembly by a support arrangement which permits the chair seat to pivot relative to the upright assembly about a generally transverse horizontal axis which is preferably slightly below the upper surface of the seat when the latter is in a nondeformed condition, i.e., the seat is not occupied. A tilt control mechanism is coupled between the control housing, the upright assembly and the seat frame so as to permit synchronized tilting of the seat relative to the back in response to tilting of the back about the axis of the tilt shaft.
With the improved arrangement of the present invention, as briefly summarized above, rearward tilting of the chair back, and relative but synchronized tilting of the chair seat, as controlled by the tilt control linkage which is coupled between the chair back and seat and the stationary control housing, as well as the tilt support mechanism which couples the seat to the upright assembly, enables the body of the chair occupant to more naturally flex at various joints so as to provide for improved user comfort when the chair is occupied. More specifically, during the rearward and synchronized tilting of the seat and back, both the seat and back remain in proper supportive engagement with the occupant""s body so as to effectively eliminate or at least greatly minimize any relative sliding between the occupant""s body and either the back or seat. At the same time, the occupant""s body undergoes natural flexing and opening of the angle at the ankle joint, the knee joint and the hip joint as the chair is tilted rearwardly, while enabling the occupant""s feet to remain comfortably and stably supported on the floor throughout the range of rearward tilt movement, thereby providing an improved degree of comfort to the seated occupant which is believed at least equivalent to mechanisms which provide so-called xe2x80x9cknee tiltxe2x80x9d or xe2x80x9cankle tiltxe2x80x9d motion.
In the improved chair of the present invention, the tiltable support of the seat on the upright assembly, so as to permit relative tilting therebetween in response to tilting of the back, is configured so that tilting of the seat relative to the upright occurs about an axis which is disposed below the normal nondeformed upper surface of the seat, whereby this axis hence is disposed approximately at the contact zone between the hip bone and the seat when the seat is occupied and deformed, thereby permitting a more natural rolling contact between the hip bone and the seat so as to eliminate or at least greatly minimize any relative sliding at the contact zone.
Other objects and purposes of the present invention will be apparent to persons familiar with chair constructions upon reading the following specification and inspecting the accompanying drawings.